1. Field of the Invention
The invention relates to a pressure gauge, more particularly to a coupling device for coupling an indicator needle to an actuating unit in a pressure gauge.
2. Description of the Related Art
A pressure gauge includes an indicator needle, an actuating unit movable in response to pressure measured by the pressure gauge, and a coupling device connected operatively to the indicator needle and the actuating unit for moving the indicator needle in accordance with movement of the actuating unit.
Referring to FIG. 1, a conventional coupling device for a pressure gauge is shown to comprise a lower positioning plate 1a, an upper positioning plate 2a connected spacedly to the lower positioning plate 1a, a sector gear 3a disposed between the lower and upper positioning plates 1a, 2a and mounted rotatably thereto, an adjustment plate 4a disposed between the lower and upper positioning plates 1a, 2a and mounted adjustably on a top side of the sector gear 3a, a push rod 5a with a first end in force-transmitting relationship with the actuating unit of the pressure gauge (not shown) and a second end connected to the adjustment plate 4a, a pinion 6a disposed between the lower and upper positioning plates 1a, 2a and mounted rotatably thereto, the pinion 6a meshing with the sector gear 3a, and a support plate 15a mounted on a bottom side of the lower positioning plate 1a for supporting distal bottom ends of a gear axle of the sector gear 3a and a pinion axle of the pinion 6a thereon. The indicator needle (not shown) of the pressure gauge is mounted on a distal top end of the pinion axle above the upper positioning plate 2a. A spiral spring 7a biases the pinion 6a to rotate the indicator needle to a starting position.
The drawbacks of the conventional coupling device are as follows:
1. The conventional coupling device cannot be conveniently assembled because too many screws and rivets are employed. For example, screws are used to mount the support plate 15a on the bottom side of the lower positioning plate 1a, while rivets are used to connect the upper positioning plate 2a to the lower positioning plate 1a. This entails a relatively large manpower cost.
2. The conventional coupling device has small components, such as the pinion 6a, which are made of copper or copper alloy. Since metal forming is a relatively complicated process, the metal components of the conventional coupling device cannot be manufactured with ease. For example, in the case of the pinion 6a, high precision forming of its gear teeth is conducted through the use of a separate, relatively expensive process, thereby increasing the costs incurred in the manufacture of the conventional coupling device.
3. Since almost all of the components of the conventional coupling device are made of copper or copper alloy, the material cost of the conventional coupling device is relatively high.